British filmmaker Bart Layton's award-winning documentary “The Imposter” revisits an unsolved San Antonio mystery and makes an implausible saga of deception seem, at the very least, not so far-fetched.

“The Imposter” is the chilling story of an unflinching, manipulative 23-year-old French con artist, Frédéric Bourdin, who took the identity of a long-missing San Antonio boy, Nicholas Barclay

Bourdin then passed himself off for months as the teenager to the boy's family even though he didn't look or sound anything like him.

Barclay was never found and is presumed dead.

“If you read it as a work of fiction, you'd think it was far-fetched in some ways,” Layton said. “It's not that I doubted everybody. It's that I believed everybody. And that's the problem.”

Layton interviews all the major characters on camera, re-creates key scenes with actors, uses flashbacks and home video. His reconstruction of an unsolved mystery long grown cold makes “The Imposter” (opening Friday) a mind-twisting psychological thriller.

San Antonio private investigator Charlie Parker, who played a major role in revealing the scam, adds down-home authority to the very strange tale.

“It was one of the scariest things I'd ever done,” Parker said. “Bourdin has an aura about him; just evil comes out of him. He's scary as hell.”

Barclay — a streetwise, hard-to-control boy, often left on his own and “not innocent,” according to his sister — was 13 when he disappeared.

That was June 1994.

Three years later, the missing boy's family received the unlikely news that Nicholas was in police custody in Spain and recounting a harrowing story of kidnapping, torture and sexual slavery and abuse.

They welcomed the imposter with open arms — and hearts. There's even home video of the moment. They would soon come to regret such kindness when the masquerade was revealed and Bourdin cruelly turned on them.

Once the jig was up, Bourdin accused Barclay's family of killing the boy and disposing of the body. A homicide case was opened but closed for lack of evidence.

Parker, who believes Barclay is dead, even went digging for a body.

“The case is not over, and I'm going to find Nicholas Barclay,” he said.

Layton was drawn to the story by an article in a Spanish magazine about the imposter, Bourdin, who survived and thrived masquerading as teenagers.

“He was already known in France as a chameleon,” Layton said. “It was compelling enough for me to find out more.”

In a New Yorker feature, writer David Grann described Bourdin as a man who could “elevate his criminality into ‘art.'”

Even so, it's hard to understand how Bourdin, who speaks English with a heavy accent and has brown eyes and brown hair, could have passed himself off in October 1997 as a blondish, blue-eyed teen several years younger.

The beauty of Layton's film is that audience members may ask not only “How could they be so gullible?” but also “Could I be that gullible?”

The filmmaker wanted to explore that question. He found Bourdin and persuaded him to participate in the film, which wasn't easy. The con man — who went to prison because of his actions — wasn't the most trusting person, Layton said.

“But he's also not a shy man,” he added. “He was willing to tell his story in his own words.”

The family was hesitant, as well.

“They felt that they hadn't come out well from the New Yorker piece,” he said, adding that a fictionalized film had hurt them, too. “They were depicted very negatively. So they were understandably very reluctant. Ultimately, they wanted to tell their side of the story.”

Layton said family members, who still live in San Antonio, accepted his “honest account.”

On camera, Barclay's older sister, Carey Gibson, can't explain how the family was fooled.

“How could I be so (expletive) stupid?” she asks.

Watching “The Imposter” it's hard to be too judgmental. After all, Bourdin fooled law enforcement officials in Spain, at the American Embassy and the FBI. And the working-class family desperately wanted to believe.

“When you hear this story, your immediate thought is, ‘How could this situation come about? How could a family fail to know their own son after three and a half years?'” Layton said.

“That's one of the biggest puzzling things. The film makes you wonder about what people are capable of convincing themselves of if they desperately want it to be true.

“It's not just about deception on the part of the imposter, but self-deception. And that's something we can all understand.”